Fluid and process for treating wells



Jan. 26, 1965 E. N. ALTER 3,

FLUID AND PROCESS FOR TREATING WELLS Filed Nov. 25, 1960 8* A; tr a m w z v9 m E q z u j 2 q m y] N j K) Q 0 8 o 8 o k 8 8 g g v N WdU oz -sd0 NI )ulsoasm g 8 8 8 8 o w 2: a: N was 02 -s=|o NI ALISOOSIA F m l "v m a Q II 8 r I u E a, Q: Q K) a: U f D ELL z "w N M I a I g L Q 0 O O 3 g 3 8 was oz-sd: NI Al I SOOS IA \J INVENTOR. o 8 8 8 o EMIL N. ALTER 8 Q Q N (D m N BYTMQ K, L, was 02 -sdo NI ALISOOSIA QM-HL'DR his ATTORNEYS United States Patent Ofifice 3,167,510 Patented Jan. 26., 1965 3,167,510 FLUID AND PROCESS FOR TREATING WELLS Emil N. Alter, Bayside, N.Y., assignor to Stein, Hall & Co., Inc., New York, N.Y., a corporation of New York Filed Nov. 25, 1960, Ser. No. 71,566 19 Claims. (Cl. 252-855) This invention relates to improved fluids for treating wells and to an improved method of breaking or of reducing the viscosity of such well-treating fluids.

Fluids of various types are used in well treating operations. One major use of fluids is in earth formation fracturing. In these procedures, the fluid is introduced into the well and forced into surrounding earth formations by application of hydraulic pressure. Fluids used in fracturing may be based on petroleum fractions as a major constituent. It is more usual, however, to employ water-based fluids containing either pure water or brine inmajor proportion.

Along with water-based fluids, it is preferred to employ an additive which imparts sufficient viscosity to the fluid to maintain entrained solids in suspension. Representative additives which are used include gelatin, starch,

assists in maintaining sand or other finely-divided solid material in uniform suspension until the material can be placed withinthe fractured earth formation as a prop.

Once this function is completed, it is desirable to reduce the viscosity of the fluid so that it may be easily removed from the formation. 'In the art, the step of reducing the viscosity of the fluid -to facilitate its removal from the producing formation is known as breaking.

This invention is particularly concerned with a method of breaking Well-treating fluids containing guar gum as a viscosity-imparting additive. Breaking is primarily done by one of twomethods. The fluid containing guar gum will break naturally by bacterial degradation or by subjection to high temperatures. These natural methods have the disadvantage of requiring a considerable length of time, 'i.'e., several days; In the case of'fluids based on brine, as long as a week may be required.

7 The second method which has found favor involves the use of enzyme preparations. effective in bringing about a rapid breaking of the'fluid, it possesses. a number of disadvantages. generally mixed with the guar gum in the dry state. This mixture is fairly stable on storage but as soon ast'he preparation is hydrated, enzyme action commences and the guar gum is hydrolyzed. The guar gum is hydrated at the surface before it is injected into the well. As long as two hours may be required to hydrate the gum, and a considerable degree of hydrolysis will take place during this step. To compensate for this loss, additional quantities of guar gum must be used initially. w

As anadditional disadvantage, enzymatic hydrolysis becomes extremely rapid at temperatures around 140 F. This is a temperature which is commonly found inwells and when it is encountered, the viscosity of the fluid may be reduced below that viscosity required for particle suspension before the particle can be forced into the earth formation.

The enzyme is While this method is I From the above discussion of the prior art, it is evident that a process which will permit full utilization of guar gum so as to maintain maximum viscosity in the fluid until the particulate solid inplaced in its desired position within the producing strata and at the same time bring about rapid breaking of the fluid immediately thereafter, has long been needed.

It has been found'that by providing for the presence of an alkali metal persulfate at a low level in aqueous well-treating fluids containing guar gum as a viscosityimparting additive, it is possible to provide a fluid which makes full utilization of the guar gum employed in regard to its viscosity-producing effect and at the same time provide a fluid which will break on subjecting the fluid to' an elevated temperature for a reasonably short period of time. Well-treating fluids basedon water arid containing guargum and a small percentage of an alkali metal persulfate may be stored for as long as 24 hours at F a normal surface temperature, without a reduction in the viscosity of the fluid. At the same time, breaking of such a fluid will occur within from one to two hours after the fluid has been subjected to an elevated temperature within the range usually found in deep wells.

The persulfate, e.g., alkali metal persulfates, which may be used according to this invention include potassium persulfate, Kzsgog; ammonium persulfate, (NHQ S O and sodium persulfate, N a S O Of these materials, potassium persulfate is preferrde.

The alkali metal: persulfates of this invention are preferably employed at a level ranging from about 0.15% to about 0.5% based upon the weight of the guar gum employed. The amount may be varied, depending upon whether brine or fresh Water is employed in the fluid, upon the temperature expected at the breaking site, and upon the time within which the desired delayed breaking is to occur. w

At lower temperatures, i.e., 80 F., the breaking'action of the preferred potassium persulfate is not appreciable in either brine or fresh Watersystems, regardless ofthe concentration employed; At temperatures above F., the degree of breaking action is dependent upon the concentration of potassium persulfate and the temperature. An increase in concentration will provide aniin-- crease in breaking action at a given temperature. Similarly, an increase in temperature above about 100 F. will increase the rate of breaking for a given concentration of persulafte. The breaking effect produced byfthe persulfates is more pronounced in fresh water than in brine systems, so that the latter may require a higher level of persulfate to produce the same result. The preferred concentration of potassium persulfate is .25

based on the weight of guar gum. An increase in pogum in the form of a complex. Potassium permanganate,

KMnOgpotassium chromate, K CrO potassium periodate, K10 potassium perchlorate, KClO sodium chlorite, NaClO calcium peroxide, CaO and sodium nitrate, NaNO are examples of oxidizing agents Whichdo not function according to this invention.

each of FIGURES 1 through 3 that the use of an enzyme breaker greatly reduces the initial solids-suspending ability of the fluid; i 1

When the fluids of this invention are. used in fracturing processes, various propping agents are suspended therein In FIGURE 3, the curves A and B are intermediate be tween those of FIGURE 1 andFIGURE 2. FIGURE 4 illustrates the differences between A and B at .176? F.

. Curve C is omitted from'this figurebecause the enzyme is .inactivated at this temperature; It is .apparent from .75 hydrated;

. The. invention may be better understood by reference prior to their introduction into the well. Sandor gravel to the drawings attached hereto, inwhich: are conventional propping agents because of their ready FIGURE 1 shows a series of curves comparing the visavailability; Other finely-divided solid materials may be cosity of three guar'gum solutions at 77 F. over a 24 used, if desired. v hour period; I 10 The following examples further illustrate the process FIGURE 2 shows a series of curves illustrating the visof this invention. 3 5 cosity of the solutions described in FIGURE 1, held at EXAMPLE 1 140 F. for a 24 hour period FIGURE 3 shows the viscosity of solutions described Table 1 below demonstrates.the effect of vafymg i in FIGURE 1 held at r a 24 fi period, and level of potassium persulfate 1n the well-treating flu ds FIGURE 4shows the viscosity of Sblutions described of this invention. The effect is demonstrated in solutions in FIGURE 1 held at F. for-a 24 w. period of tap Water and of water containing 10% of sodium In each of FIGURESd through 4 curve A repre chloride. The latter solution is employed to simulate the sents the viscosity of a 1% solution of pure guar gum; i fcund flmtis based 9 naturally Cicwrnng curve B represents the viscosity of a .l% solution of guar brme P l g u at 3 17e2vel gum containing 0.25% potassium persulfate based on the of Per V1000 gallons 0 so v weight of the guar gum; and curve C represents the viswelght' i i cosity of a 1% solutionof guar gum containing sufficient Tableglves P y' measurements m determmed" enzyme preparation to'efiect a complete breakby a 'Brookfield viscosimeter operated at 20 rpm. The I Referring to FIGURE 1, it will be noted that the vis- Solutions were prpared by hydratmg the gum gum cositv of the guar gum solution containing potassium W hours at room temperature Thereafler S0111 persulfate was the same over a 24 hour period as the Hons were heated on Steam h for six P E to viscosity of a pure guar gum Solution" The viscosity obtain an initial reading and thenaged at the indicated of a guar gum solution containingrthe enzyme prepara temperatures for the indicated periods :of time. v 5 tion, however, was initially only about-one-half the vispotflssmm Persulfate femployec} a Pamela SIZE cosity of the pure guar gum solution and the viscosity OI PP P Y 20 m Wlth the @F u of that rapidly decreased f th t i t 'ployed in Samples 25 and Potassium persulfate hav- In FIGURE 2, when the various solutions were held 5 mg a Partlcle $126 of mesh Was p y 1n latter at 140 F., the pure guar gum solution maintained a high two samples. 7 r

- Table 1 Sample' u IIe'rSceCnt Medium 27hr. cb i a tfivlin. 1117. 2111. 24 hr. 48 hr .02 hr. 72 hr 170m. 214mmp- 2 2 s' 150. p a ernp. 0.25 860 V 0.5 860 .880 .900 900 so 0. 5 820 6. 4 820 880 880 940 so 1. 0 840 0. 4 840 880 880 900 so 0. 25 800 7. 4 800 880 880 870 28 t3 :2 ii 2; 2s 22s "23 0125 860 e15 050 720 730 070' r 100 0. 5 820 0. 4 600 680 700 640 100 1. 0 840 6. 4 600 680 720 070 100 '0. 25 800- 7.4 000 a 700 700 10 100 0.5 7800 7.4 .000 660 050 80 100 i. 0 800 7. 2 000 050 040 00 150 0.25 860. 0.5- 364 420 420 150 1 50 0. 5 820 6. 4 300 420 410 158 150 840 6.4 300 r 420 390 0. 25 '800 7. 4 308 274 190 4 150 0.5 800 7.4 282 180 104 2 150 i. 0 800 7. 2 24s 90 .42 2 200 0.25 800 0.5 250 11,6 55. 8, 200 0. 5 820 0. 4 256 106 38 10 200 1. o 840 6. 4 254 I 70 18 2 200 0. 25 800 7. 4 .10 0 200 0.5 800 7.4 80 8 0 0 200 1.0 800 7.2 40 0 .4 0 150 0. 25 800 6.9 305 v294 210 10 s 150 0.25 200 0.5 350 390 370. 158 95 r 39 viscosity for approximately two hours and then slowly 60 V I 7 EXAMPLE 2 g gg z s i gp g zg t? ebemg requlred the Tables} and 3 belowdemonstrate the breaking effect Pr a r m, of potassium persulfate on guar gum' soltuions. Solu- The solution containing potassium persulfate however, fi were prepafgd containing 1% of gumm WP/tamed hlgh approxlmately 9116 hour: tilled water and these solutions were hydrated for 30. Durmg the next hour the vlscositY p i i 65 minutes at room temperature. Monethanolamine' was gfig g rts gg t igi/igfiggfig? fr l vt l lz glzg g ugi g zl rg employed at the levels indicated: in .order to increase. V j the rate of hydration of the guar gum; at room temperaft 24 hours- The guarygum contam' ll ture. At the end of 30 minutes, the samples were immeez mg enzyme 'a 'F m 10W S W- f fi fi V diately broughtfto the indicated temperature. The tables, hour, an the cosity rapidly dropped off from this PQ 7 0 give viscosity measurements determined on a Brookfield;

viscosimeter operated at 20 rpm. The levels of the additives given are'based on the weight of the guar gum; V The viscositieswere determined at the 'agingtempera-i 4 ture.

In Table 3, the additives were added as, the sample,

g Table 2 Sample I II III 5 Percent 'Monoethanolamine- -.i 0. 3 0. 3 Percent K SzOn 0.05 0. 15 old 2 hr. pH 6. 8 7. 8 7. 9 Cold 24 hr. pH 4. 9 5. 15 4. 9

AGED AT 25 0.

30 Minutes 1,700 1, 840 2, 010 GQMinutes- 200 2, 300 2, 380 120 Minutes- 2, 480 2, 560 2, 590 240 Minutes. 2, 650 2,700 2, 690 24 Hours 2, 560 2, 370 2,100

AGED AT 40 0.

30 Minutes 1,900 2,020 2, 040 60 Minutes 1, 950 2, 020 1, 970 120 Minutes.-. 1, 920 2, 000 1, 840 240 Minutes- 1, 920 1,820 1, 530 24 Housin 1,020 900 180 AGED AT 60 0.

Minutes 1, 700 1,940 1,880 60 Minutes- 1, 640 2,000 1, 830 120 Minutes 1,450 1,820 1, 400 240 Minute 990 1,280 440 24 Hours 100 g 62 2O AGED AT'80 0.

30 Minutes; 1,760 2, 040 1,800 60 Minutes 1, 760 1, 980 1, e40 120 Minutes 1, 500 1,830 900 240 Minutes. 640 680 80 35. 24 Hours 16 15 14 Table 3 Sample 40 IV- v VI Percent Monoeth'anohmine" '0. 3 0. 3 Percent K,s2og 0. 25. 0. 5 2. 5 Cold 2 hr. 5. 8' 8.75 Cold 24 hr. pH 5.6 7. 7

AGED AT 25 0. r

30 Minutes 60 Minutes 120 Minutes 240 Minutes--- 2 2 1 El) AT 40 0 AG 30 Minutes 1, 970 1, 940 Minutes. 120 Minutes 1, 940 2,110 240 Minutes 1,820 2,100 24 Hours 52 60 AGED AT 60 0 30 Minutes- 1, 950 1,800 1, 700 60 Minutes- 120 Minutes 1, 990 800 78 240 Minutes..- 110 20 10 24 Hours 15 10 I claim:

rapidly the viscosity of the fluid to a value below the initial viscosity at the relatively high temperature inside;

2. The well-treating fluid of claim 1 wherein the persulfate is potassium persulfate.

3. An aqueous well-treating fluid comprising water; hydrated guar gum in an amount sufficient to impart initially a high viscosity to the fluid; a particulate solid propping material in suspension in the fluid; and a persulfate selected from the group consisting of ammonium persulfate and an alkali metal persulfate in an amount suflicient to break rapidly the viscosity of the fluid below the initial viscosity at the relatively high temperature inside the well after the propping material is placed Withoutreducing previously the viscosity of the fluid at the relatively low temperature at the surface of the well.

4. The well treating fluid of claim 3 wherein the'persulfate is potassium persulfate.

5. An aqueous well-treating fluid comprising water;

hydrated guar gum in an amount suflicient to increase the viscosity of the fluid to a certain initial value; a particulate solid propping material in suspension in the fluid; and from .15 to .5% by weight of the guar gum of a persulfate selected from the group consisting of ammonium persulfate and an alkali metal persulfate to break rapidly the vicosity of-the fluid to a value below the initial viscosity at the relatively high temperature inside the well after the propping material is placed without reducing previously the viscosity of thefluid at the relatively low temperature at the surface of the well.

6. The Well-treating fluid of claim 5 wherein the persulfate is potassium persulfate.

7. An aqueous well-treating fluid comprising brine; a particulate solid propping material; guar gum in an amount suflicientto impart initially a high viscosity to the fluid; and a persulfate selected from the group consisting of ammonium persulfate and an alkali metal persulfate in an amount suflicient to break rapidly the viscosity of the fluid below the initial viscosity at the relatively high temperature inside the well after the propping material is placed without reducing previously the viscosity of the fluid at the relatively low temperature at the surface of the Well.

8. The well-treating fluid of claim 7 wherein the persulfate is potassium persulfate. 1

9. An aqueous well-treating fluid comprising brine; hydrated guar gum in an amount suflicient to impart initially a high viscosity of the fluid; a particulate solid propping material in suspension in the fluid; and from .15 to .5 by weight of the guar gum of a persulfate selected from the group consisting of ammonium persulfate and an alkali metal persulfate to break rapidly the viscosity of the fluid below the initial viscosity at the relatively high temperature inside the well after the propping material is placed without reducing previously the viscosity of the fluid at the relatively low temperature at the surface of the well.

10. The well-treating fluid of claim 9 wherein the persulfate is potassium persulfate.

11. An aqueous well-treating fluid comprising water; hydrated guar gum in an amount suflicient to impart initially a high viscosity to the fluid; a particulate solid propping material in suspension in the fluid; and from .15% to .5% by weight of guar gum of a persulfate selected from the group consisting of ammonium persulfate and an alkali metal persulfate; said fluid being capable of having a constant high viscosity at the surface temperature of the well; said fluid being capable of having its viscosity rapidly reduced subsequently to below the initial viscosity at the higher temperature inside the F. attlle surface of the well. 7 it 14. The method of claim 13 wherein the persulfate is sure to the fluid and producing the Well which comprises;

the step of introducing into the well" a fluid comprising water, guar' gum in an amount .suflicie'nt to impartini-- tially a high viscosity: to the fluid and fron .15% to: .5 by weight of guar gum of a persulfate selected from.

' the group consisting of ammonium persulfate I alkali metal persulfate to break rapidly the; IVlSCOSlQbOfI the" fluid below the initial Viscosity at "thejrelatively high.

temperature inside the well after a particulate solid prop' ping material is placed without reducing previously the:

viscosity of the fluid at the relatively low temperature.

at thesurface of the well.

'13. A method for treating wells to project fluid 11110 formationssurrounding the well by application of pres-L sure to the fluid and producing the well which comprises the step of introducing into the well a fluid comprising;

water, guar gum in an amount suflicient to impart inivtially a high viscosity to the 'fluid and'from .15% to- .5% by weight of guar gum of a persu lfate selected from the group consisting of ammonium persulfate and an;

alkali metal persulfate to break rapidly the viscosity of the fluid below the initial viscosity at the temperatureof about 140 C. inside the well after a particulate solid propping material is placed without reducingpreviously the viscosity of the fluid at the temperature of about 80? potassium persulfate.

15. A method for treating wells which comprises the steps of introducing into' a well an aqueous fluid comprising water, hydrated guar gum in an amount sufficient to impart initially a high viscosity to the fluid, a particulate solid propping material in suspension'in the fluid and from .15% to .5% by weight of gular gum ofa persulfate selected from the group consisting of ammonium persulfate and an alkali metal persulfate to break I below the initial; viscosity at=the 140 F. temperature" rapidly the viscosity of the fluid below thejinitial viscosity 7 at'the relatively high temperature inside the well after 7 the propping material is placed without reducing previously the viscosity of the fluid at the relatively low -tem'- perature at the surface ofthe well; projecting the fluid into formations surrounding the well by application of pressure to the fluid; and producing the well. V

. 16. The method of claim 15, wherein the per-sulfate is potassium persulfate.

17. A method for. treating wells which comprises prearing a breaking fluid comprising water, hydrated guar gum in an amount sufltcient to impart initially a high viscosity to the fluid, a particulate solid propping mate- -1'ialin the fluid and 15% to .5 by weight of guar'gum .of a persulfate selected from the group consisting of ammonium .persulfate and an alkali metal persulfate, said fluid having ,a constant high viscosity at the surface tions surroundingilthe.welllby application ofpressure .to

temperature of the wellfprojecting said fluid intoj formathe fluid; plajcingisaid propping material, said fluid havinga .rapidlyreduced viscosity below'the initial viscosity at the higher temperature inside the well subsequent to the placing of said proppingzmaterial; removing, said fluid with reduced viscosity from said well; andproducingthe v '18. A method for treating well-swhi h comprises paring a breaking fluid comprisingpwater, hydrated guar. gum in an amount suflicient .to impart initially a high viscosity to the fluid, a particulate solid propping material in suspension'in the fluid and from .15..% to .5%' byweight ofguar gum of a-persuliate selectedfrorrr thegroup consisting of ammonium persulfate and an alkali metal persulfate, said fluid having constant viscosity at i the F. surface temperature of the wellyprojecting.

the fluidinto formations surrounding the well by application of pressure to the fluid; placing said pre ng material, said fluid having a rapidly reduced viscosity;

inside the well subsequent to the placing .of saidi propping material; removing said'fluid with reduced visco'sity from said well; and producing the well. i

' 19. A. method for treating wells which comprises pre j 1 paring a breaking fluid comprising water, hydrated guatr gum inan amount sufficient to impart initially a high viscosity tothe fluid, a particulate" solid propping mate'- rial in suspension in the fluid andfrom .15 to .5 by

weight of guar gum of potassium persulfat'e, said fluid having aconstant high viscosity at the 8 0'? surface 7 temperature of the. well; projecting the fluid into for mations surrounding the well by application ofpressure to the fluid; placing said propping material, said fluid having a rapidly reduced viscosity below 'the initial viscosity at the F. temperature inside the well withini4 hours:

and subsequent to the placing of said propping material; removing'said fluid with reduced viscosity from said well;

and producing'the well. i 7

References Cited in the file of this patent V UNITED STATES PATENTS 1,873 ,63 1

OTHER' REFERENCES Gregory; Uses and Applications of ChemicalsQand Related Materials, published 1939 by Reinhold PubICo;

' of New York, .vol. 1, page 484. 

1. AN AQUEOUS WELL-TREATING FLUID COMPRISING WATER; A PARTICULATE SOLID PROPPING MATERIAL; GUAR GUM IN AN AMOUNT SUFFICIENT TO INCREASE THE VISCOSITY OF THE FLUID TO A CERTAIN INITIAL VALUE; AND A PERSULFATE SELECTED FROM THE GROUP CONSISTING OF AMMONIUM PERSULFATE AND AN ALKALI METAL PERSULFATE IN AN AMOUNT SUFFICIENT TO BREAK RAPIDLY THE VISCOSITY OF THE FLUID TO A VALUE BELOW THE INITIAL VISCOSITY AT THE RELATIVELY HIGH TEMPERATURE INSIDE THE WELL AFTER THE PROPPING MATERIAL IS PLACED WITHOUT REDUCING PREVIOUSLY THE VISCOSITY OF THE FLUID AT THE RELATIVELY LOW TEMPERATURE AT THE SURFACE OF THE WELL. 